A solution of equal parts bleach and water safely cleans asphalt shingles, according to the Asphalt Roofing Manufacturers Association. The diluted bleach cleans most effectively when applied with a pump sprayer and left on the shingles for 15 to 20 minutes.
Another way to clean shingles with bleach is to combine 1 gallon of water with 1 quart bleach and 1/4 cup trisodium phosphate, according to Today's Homeowner.
It is very important to rinse the shingles before the bleach solution dries, notes the Asphalt Roofing Manufacturers Association. A garden hose is the best tool for this job, as pressure washers can damage asphalt shingles.